Make TaskExecutionAutoConfiguration#applicationTaskExecutor lazy

[snicoll]

The creation of the bean itself is not costly as it does not hold/create any thread until a task is actually submitted to it but it logs twice at INFO level: once on startup and once on shutdown.

Given we've tried to polish and clean logs in 2.1, I think it would be worthwhile to look if we can't make that bean lazy.

[ayudovin]

As far as I understand we can just add @Lazy on creating bean ThreadPoolTaskExecutor, right?

[mbhave]

Closing in favor of PR #14934.